1. Field of the Invention
The present invention relates to display devices, and more particularly, to a display device which can provide clear contents.
2. Discussion of the Related Art
Recently, different kinds of flat display devices are under development for reducing a weight and a size which are disadvantages of a cathode ray tube.
In the flat display devices, there are liquid crystal display (LCD) devices, field emission display devices, plasma display (PDP) devices, electro-luminescence (EL) display devices, and so on. Research is underway for improving a display quality of the flat display device and making a screen size of the flat display device greater.
Of the flat display devices, the LCD device is a non-light emitting type display device which produces an image by using a light source such as a lamp, displays information by using electro-optical properties of liquid crystal injected in a liquid crystal display panel, and has advantages in that a small sized display device can be fabricated, and the display device has light weight and a low power consumption.
That is, different from the cathode ray tube, since the liquid crystals injected between a TFT substrate and a color filter substrate is not a light emitting substance, but a light-receptive substance which controls a quantity of external light incident thereon and displays the light controlled thus on a screen, an additional device for directing the light to the liquid crystal display panel, i.e., a back light assembly, is required.
In the back light assembly, there are a direct-lighting type back light assembly, and an edge-lighting type back light assembly, wherein the direct-lighting type back light assembly has the lamps under the liquid crystal display panel, for direct lighting of an entire surface of the liquid crystal display panel, and is disadvantageous in that power consumption and a production cost is high, and thickness is thick. In comparison to this, the edge-lighting type back light assembly has lamps at one or opposite sides of the liquid crystal panel for lighting the liquid crystal display panel with a light diffused by using a light plate and reflective plate, and uses cold cathode fluorescent lamp CCFL as the lamp mostly, and is advantageous in that thickness is thin to have a light weight and power consumption is low, to use widely. However, the edge-lighting type back light assembly requires the light plate for guiding the light from a side thereof to a front side thereof.
The edge-lighting type back light assembly is provided with a mold frame having a holding space formed therein, a reflective sheet on a bottom surface of the holding space for reflecting the light toward the liquid crystal display panel, the light plate on the reflective sheet for guiding the light, a lamp unit between the light plate and a side wall of the holding space for emitting the light, optical sheets stacked on an upper surface of the light plate for diffusing and converging the light, an a top sash on a top of the mold frame for covering from a predetermined portion of edges of the liquid crystal display panel to a side of the mold frame.
The optical sheets may have a diffusing sheet for diffusing the light, prism sheets stacked on an upper surface of the diffusing sheet for converging and forwarding the light diffused thus to the liquid crystal display panel, and a protective sheet for protecting the diffusing sheet and the prism sheet.
FIG. 1 illustrates a section of a related art liquid crystal display device schematically, and FIG. 2 illustrates a section of the upper polarization sheet in FIG. 1.
Referring to FIG. 1, the related art liquid crystal display device is provided with a back light unit 10 for emitting a light, a lower polarization plate 20 on the back light unit 10, a liquid crystal display panel 30 on the lower polarization plate 20 for displaying an image, an upper polarization plate 40 on the liquid crystal display panel 30, and a sheet of toughened glass 60 bonded to the upper polarization plate 40 with an UV pressure sensitive adhesive 50.
Referring to FIG. 2, the upper polarization plate 40 is provided with a release film 41, first tri-acetyl cellulose TAC 43 bonded to the release film 41 with a pressure sensitive adhesive PSA 42, an elongated poly vinyl alcohol PVA film 44 on the first TAC 43, a second TAC 45 on the PVA film 44, and a DBEF (Dual Brightness Enhancement Film) 46 on the second TAC 45 for enhancing brightness of the liquid crystal display panel 30.
In the meantime, the lower polarization plate 20 is provided the same with the upper polarization plate 40 except the DBEF 46.
The related art liquid crystal display device is susceptible to scratch due to low hardness of the DBEF 46 in the upper polarization plate 40. For supplementing this, the toughened glass 60 is bonded on an entire surface of the liquid crystal display panel.
However, the related art liquid crystal display device has a surface which is not mirror smooth due to a rugged surface of the DBEF-polarization plate which becomes poorer after bonding the toughened glass thereto such that the related art liquid crystal display device can not be used, not only as a mirror, but also as a display device.
That is, in order to solve the scratch problem, though the toughened glass is bonded to the entire surface of the liquid crystal display panel, and, in order to remove an air gap between the liquid crystal display panel and the toughened glass, the UV pressure sensitive adhesive is applied and an UV beam is directed thereto to solve the scratch problem, the ruggedness of the surface of the display becomes more intensive such that the related art liquid crystal display device can not be used, not only as a mirror, but also as a display device.
In the meantime, the ruggedness of a raw material of the polarization plate becomes the more intensive as a size of the panel becomes the larger, and the bonding between the polarization plate and the rugged portion of the pressure sensitive adhesive forms grain enough to see with naked eyes.